2
$\begingroup$

Looking around the web, I see some submerged bucket-like things, without insulation, and some floating coolers, where the actual cooler is not submerged.

Given that your water temperature is lower than the air temperature, would a mostly submerged, insulated cooler keep cold, inside, longer? Would the heat exchange be hastened by the conductivity of the water or slowed by the improved temperature differential between inside/outside the cooler?

Summertime sea temp near Seattle is 52$^{\circ}$F. Lakes are warmer, maybe 60-65$^{\circ}$F. On a summer day, the air temp might be 65-75$^{\circ}$F.

To clarify, I have a cooler with beer and ice inside, hopefully around 40$^{\circ}$F. I want to keep that beer as cold as possible, for as long as possible.

$\endgroup$
  • $\begingroup$ It depends on what you mean by colder. If you want to keep it at $52^\circ$, then submerging it in the sea will keep it at that temperature indefinitely. $\endgroup$ – Chris Mueller Jul 17 '14 at 16:35
  • $\begingroup$ Yes, I realize I can keep it at 52*, just by sticking the beer in the water. However, in a cooler, packed correctly with ice, you can get approximately 40* or less. $\endgroup$ – Doug Cassidy Jul 17 '14 at 17:07
  • 1
    $\begingroup$ Water has a lot more thermal mass to pour heat into your cooler than air. $\endgroup$ – Oldcat Jul 17 '14 at 17:25
  • $\begingroup$ What works better than a cooler is a good waterproof winter jacket and a good winter sweater. Turn both the jacket and the sweater inside out and put the jacket inside the sweater.Put this in a rucksack and then you put the beer and ice inside the jacket. This works better and is much easier to carry than a bulky cooler loaded with beer. If the winter gear is good enough to keep you warm and comfortable at -20 C with strong winds, this is guaranteed to keep your beer cool for a long time when it is very warm outside. $\endgroup$ – Count Iblis Jul 17 '14 at 17:51
  • $\begingroup$ In a cooler packed with ice you can hit $32^\circ$. My point was that you should be a little more specific in your question about your definition of colder. $\endgroup$ – Chris Mueller Jul 17 '14 at 18:43
1
$\begingroup$

A cooler that has ice and water in it will be held at 32 degrees Fahrenheit until all the ice is melted. The rate at which the ice melts depends on the rate at which heat can enter the container.

The rate at which heat crosses any thermal boundary can be modeled as:

$$\dot Q=\frac{\Delta T}{\sum 1/h_i}$$

Where $h_i$ represent the thermal conductivity of each thermal resistance. In the case of the cooler there will be a thermal resistance due to the cooler. A thermal resistance due to the transition from liquid inside the cooler to the cooler wall, and finally an transition between the cooler outside and the outside medium.

This outside thermal resistance changes depending of whether the medium is air or water. A typical value for still air is around $5 \frac{W}{m^2K}$, while a typical value for water is $100\frac{W}{m^2 K}$.

Now if we assume the cooler can be approximated as 4cm thick Styrofoam then it would have a h of $0.8 \frac{W}{m^2 K}$. So the thermal resistances of the cooler in the two scenarios are:

$$\frac1{100}+\frac1{0.8}+\frac1{5}=0.01+1.25+0.2=1.45$$ $$\frac1{100}+\frac1{0.8}+\frac1{100}=0.01+1.25+0.01=1.26$$

So the air version would insulate 1.15 times better.

The temperature differences however would drive the heat with $\frac{75-32}{52-32}=2.15$ times the temperature difference. So on a warm summer day the sea would keep your cooler contents cool 1.9 times longer.

Note that a 4cm thick Styrofoam cooler is actually quite a nice cooler. If you don't have such a nice cooler, it might be better to keep the cooler out of the water, but if you don't have a nice cooler, the ice is gonna melt pretty fast no matter where you put it.

$\endgroup$
  • $\begingroup$ I think what youre saying is that where the air/sea temp is the same, I'd be better off with the cooler out of the water. However with air @ 75* and sea @52*, the sea would keep beer colder almost twice as long. Approximately what sea temp would be the breaking point to where air is better? For instance, we have lakes, which are about 60-65*. $\endgroup$ – Doug Cassidy Aug 31 '15 at 21:40
  • 1
    $\begingroup$ @DougCassidy Depends on the cooler. For the 4cm thick Styrofoam the temp difference would need to have a ratio of 1.15 to break even so it were 75 in the air, that would be (75-32)/1.5+32=60.6 degree water. For a thinner cooler the break even temperature would be lower as the ratio of insulation would be larger. $\endgroup$ – Rick Sep 1 '15 at 17:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.